Spectroscopic techniques including but not limited to dynamic light scattering, photon correlation spectroscopy and fluorescence correlation spectroscopy have been adopted for studying strongly scattering media such as colloids, gels and tissues. The techniques mentioned above are derived from Rayleigh scattering and/or fluorescence phenomenon. One of the advantages of multiple Rayleigh scattering in strongly scattering media has been the study of dynamics of particles in motion in any given sample. Also the multiple Rayleigh scattering enables estimation of the size distribution of particles in the sample. Another application of Rayleigh scattering has been in areas including but not limited to non-invasive depth profiling and neuro-imaging. However, the scattering profile does not identify the type of materials present in the sample.
Since the multiply scattered light contains both Rayleigh and Raman scattered photons, recording Raman scattered light has been explored for identifying the structure and chemical nature of the molecules. Examples of known techniques that record Raman scattering include but are not limited to Spatially Offset Raman Spectroscopy (SORS), Surface Enhanced Raman Spectroscopy (SERS) and transmission Raman spectroscopy (TRS). SORS works on the principle of backscattering collection geometry wherein the scatterers close to the surface contribute more to the Raman signal than the scatterers located deeper in the sample. SERS works on the principle of Raman light amplification in the presence of a noble metal surface that results in chemical and surface plasmon resonance enhancements of the incident electromagnetic field. One of the primary disadvantages of SORS, SERS and TRS is that the detection is restricted to a specific experimental geometry. For example, SORS works only in the backscattering geometry; SERS relies on metal surface for amplification and TRS cannot distinguish the individual layers of different chemicals in a multi-component layered system. Further, the depth at which detection is effective is limited up to few mm, for example 3 mm. Hence, there is a need for method that can profile samples at various levels of depth.